The banjo was developed in the Americas by the enslaved persons from Africa. Because of the nature of the slave trade, the enslaved did not bring instruments from Africa, rather used available materials to construct similar instruments. Major differences included a flat neck on the American banjo rather than the round stick of the African Spike lutes, and the way that the neck was inserted through holes in the body of the gourd for stabilization rather than the round stick placed on top of the gourd and held in place by the skin head.
The earliest reference from 1678 mentions a "banza" in Martinique. From this point forward there is consistent reference to the instrument in historical documents. In 1781 Thomas Jefferson wrote: "The instrument proper to the [slaves] is the Banjar, which they brought hither from Africa."
From the 1830's through the 1860's the 5 string banjo was used in minstrel shows, an early form of American Popular music, played in the "stroke" style with the back of a finger and the thumb. The Reconstruction following the Civil War began a period of increasing wealth in the middle class. Banjos became a popular mail order item. Following an interest in European style parlor music, classical guitar finger-style technique was developed for the banjo to replace the old minstrel "stroke" style. Classical and popular American parlor music was adapted to this style. Many high quality instruments were manufactured in Boston, and New York, setting a standard that is emulated today.
In England during the "Classic" period, it was common to add strings so that 6 or 7 string "zither" banjos were played. The finger-style banjo remained popular in the U.S. until the early 1900's when the jazz era ushered in the popularity of the four-string tenor which would become the favored instrument of the period. The 5-string banjo once again began to overshadow the tenor as Bluegrass music exploded out of the south, fueled by radio, records, television, and movie sound tracks. The 5-string banjo found its way into the cities of the Northeast in the great folk music revival of the late 1950's and 1960's with young virtuosos recording and writing widely published modern methods for the instrument.
For more information and pictures of banjos through out the centuries, see the Smithsonian Banjo Spotlight.
For a discussion about what is a Classic Banjo see the Classic Banjo website FAQ.